Atomic Structure
The nuclear atom
Electron Configuration
Ms. Thompson - SL Chemistry
Wooster High School
Wednesday, July 15, 15
Topic 2.1
The nuclear atom
•
•
•
Atoms contain a positively charged dense nucleus composed of
protons and neutrons (nucleons).
Negatively charged electrons occupy the space outside the
nucleus.
The mass spectrometer is used to determine the relative
atomic mass of an element from its isotopic composition.
Wednesday, July 15, 15
The nuclear atom
Subatomic particles and descriptions of the atom
•
Atoms consist of three types of subatomic particle:
• proton
• neutron (discovered by British physicist James Chadwick, 1932)
• electron
• Masses are in atomic mass units (amu)
-24g
1
amu
=
1.660539
x
10
•
Subatomic
Particle
Charge
Mass/amu
Location
proton
+1
~1
nucleus
neutron
0
~1
nucleus
1/1836
outside nucleus in
electron cloud
electron
Wednesday, July 15, 15
-1
Wednesday, July 15, 15
Wednesday, July 15, 15
The nuclear atom
Subatomic particles and descriptions of the atom
• The atomic number, Z
• Atoms each have their own unique atomic number, Z
• The atomic number is the number of protons in the nucleus of the
•
atom of an element.
In a neutral atom (no overall charge) the number of electrons is equal to
the number of protons.
• Z for oxygen is 8, oxygen has 8 protons and 8 electrons
(-8)+(+8) = 0 (neutral)
• The mass number, A
• The mass of the atom comes from the nucleus, which contains the
•
•
•
protons and neutrons.
The mass number, A, is the number of protons + number of neutrons
Z for fluorine, F, is 9, fluorine has 9 protons and 9 electrons
A for fluorine-19 is 19. Therefore, fluorine has 19-9=10 neutrons
Wednesday, July 15, 15
The nuclear atom
Subatomic particles and descriptions of the atom
•
•
The nuclear symbol includes both A and Z for a particular
element X and is represented like this:
A
ZX
Isotopes are different forms of the same element but have
different number of neutrons (different mass numbers, A)
•
Hydrogen has three isotopes:
3
1H
(tritium)
1 proton, 1 electron, 2 neutrons
2
1H
(deuterium)
1 proton, 1 electron, 1 neutron
1
1H
(hydrogen)
1 proton, 1 electron, 0 neutrons
Wednesday, July 15, 15
The nuclear atom
Isotope enrichment: Nuclear energy and nuclear weapons
Uranium found in nature consists of three isotopes with the relative abundances and atomic
composition found below:
Isotope
234U
Relative Number of Number of Number of
abundance
protons
electrons
neutrons
0.0055%
92 protons
92 electrons 142 neutrons
235U
0.7200%
92 protons
92 electrons
143 neutrons
238U
99.2745%
92 protons
92 electrons
146 neutrons
Uranium-235 is used in nuclear reactors where it undergoes fission (splitting) with the
release of a large amount of energy. Natural uranium has a much higher abundance of U-238
than U-235 so uranium ore may be enriched to increase the proportion of U-235. The
separation of natural uranium into enriched uranium and depleted uranium is the physical
process of isotope separation.
Because they are the same element, the isotopes have the same chemical properties but they
show different physical properties due to their different mass numbers.
Wednesday, July 15, 15
The nuclear atom
Radioisotopes
•
•
Boron has numerous radioisotopes (radioactive isotopes)
• Boron-10, Boron-11, Boron-8, Boron-9, Boron-12, Boron-13
Radioisotopes are used in nuclear medicine for diagnostics,
treatment, and research.
• Iodine-131 is used as a tracer for thyroid issues
• Carbon-14 is used for age determination in archaeology,
geology, geophysics, and other branches of science
Wednesday, July 15, 15
The nuclear atom
Mass spectrometer
Wednesday, July 15, 15
Mass Spectrometer
Process
vaporization
ionization
acceleration
deflection
detection
Equipment
vaporizer
ionizer
accelerator
deflector
detector
Details
the atom is
changed into a
gaseous state
the atom is
bombarded
by a beam
of
electrons
to form
positive
ions
the positive
ions will pass
through an
electrical field
where it will
be accelerated
the positive
ions will
pass
through a
magnetic
field where
the lighter
ions will be
deflected
more than
the heavier
ions
the
difference
ions will be
detected
Wednesday, July 15, 15
Practice Problem
... I Do ...
Boron has two naturally occurring isotopes with
the natural abundances shown below:
Isotope
Natural Abundance/%
10B
19.9
11B
80.1
Calculate the relative atomic mass of boron:
19.9
80.1
relative atomic mass = (10 x
) + (11 x
) = 10.8
100
100
Wednesday, July 15, 15
Practice Problem
... We Do ...
Rubidium has a relative atomic mass of 85.47 and consists of
two naturally occurring isotopes, 85Rb (u=84.91) and 87Rb
(u=86.91). Calculate the percentage composition of these
isotopes in a naturally occurring sample of rubidium.
84.91x + 86.91(100-x)
Ar = 85.47 =
100
85.47 x 100 = 84.91x + 86.91(100-x)
8547 = 84.91x + 8691 - 86.91x
-2.00x = -144
x = 72.00
The sample contains 72.00% 85Rb and 28.00% 87Rb
Wednesday, July 15, 15
Practice Problem
s
... You Do ...
Work with a partner and
answer the following
question:
Deduce the relative atomic mass
of the element X from its mass
spectrum (right) and identify X
from the periodic table.
Hint: X-69 and X-71
Hint: 27 & 71 = peak heights
45
40
35
relative abundance
in
20 m
30
25
20
15
10
5
69
0
0
Wednesday, July 15, 15
20
40
60
m/z
71
80
100
Topic 2.1
The nuclear atom
➡Atoms contain a positively charged dense nucleus composed of
protons and neutrons (nucleons).
➡Negatively charged electrons occupy the space outside the
nucleus.
➡The mass spectrometer is used to determine the relative
atomic mass of an element from its isotopic composition.
Wednesday, July 15, 15